The Volcanic Explosivity Index (VEI) is a relative measure of the explosiveness of volcanic eruptions. It was devised by Chris Newhall of the United States Geological Survey and Stephen Self at the University of Hawaii in 1982. Newhall and Self, 1982

“……Volcanologists believe a Yellowstone supereruption would bury large swaths of Colorado, Wyoming and Utah in up to three feetof toxic volcanic ash. Depending on the weather patterns, much of the Midwest would receive a few inches, too, plunging the region into darkness. Even the coasts — where a majority of Americans live — would most likely see a dusting as the ash cloud spread. Crops would be destroyed; pastureland would be contaminated. Power lines and electrical transformers would be ruined, potentially knocking out much of the grid...….That’s just the United States. Modeling by meteorologists has found that the aerosols released could spread globally if the eruption occurred during the summer. Over the short term, as the toxic cloud blocked sunlight, global average temperatures could plunge significantly — and not return to normal for several years. Rainfall would decline sharply. That might be enough to trigger a die-off of tropical rain forests.….”

‘…….“The potential for damaging earthquakes, landslides, floods, tsunamis and wildfires is widely recognized in California,” another recent USGS report reads. “The same cannot be said for volcanic eruptions, even though they occur in the state about as frequently as the largest earthquakes on the San Andreas Fault.”

Of the state’s eight volcanoes, seven have been found to sit above “active” magma chambers.

Disturbingly, it finds some 200,000 people are classified as “at-risk” if an eruption was to occur. And it argues there is a 16 percent chance of such an event within the next 30 years.

Like the fault-line studies, geologists have pulled clues from California’s landscape to determine volcanic activity over the past 5,000 years.

It’s found five volcanoes – Mount Shasta, Medicine Lake, Lassen, Long Valley and Salton Buttes – have erupted during the past 3000 years. Clear Lake Volcanic Field near San Francisco – while rated as potentially of very high risk – hasn’t blown for longer…….’

The dormant period ended around 4:00 a.m. local time on June 22, 2019, when a vast plume of ash and volcanic gases shot up from its 700-meter-wide crater. Several satellites—as well as astronauts on the International Space Station—observed as a thick plume rose and then streamed east as it was pulled into the circulation of a storm in the North Pacific.

On the morning of June 22, astronauts shot a photograph (above) of the volcanic plume rising in a narrow column and then spreading out in a part of the plume known as the umbrella region. That is the area where the density of the plume and the surrounding air equalize and the plume stops rising. The ring of clouds at the base of the column appears to be water vapor.

“What a spectacular image. It reminds me of the classic Sarychev Peak astronaut photograph of an eruption in the Kuriles from about ten years ago,” said Simon Carn, a volcanologist at Michigan Tech. “The ring of white puffy clouds at the base of the column might be a sign of ambient air being drawn into the column and the condensation of water vapor. Or it could be a rising plume from interaction between magma and seawater because Raikoke is a small island and flows likely entered the water.”

Since ash contains sharp fragments of rock and volcanic glass, it poses a serious hazard to aircraft. The Tokyo and Anchorage Volcanic Ash Advisory Centers have been tracking the plume closely and have issued several notes to aviators indicating that ash had reached an altitude of 13 kilometers (8 miles). Meanwhile, data from the CALIPSO satellite indicate that parts of the plume may have reached 17 kilometers (10 miles).

In addition to tracking ash, satellite sensors can also track the movements of volcanic gases. In this case, Raikoke produced a concentrated plume of sulfur dioxide (SO2) that separated from the ash and swirled throughout the North Pacific as the plume interacted with the storm.

“Radiosonde data from the region indicate a tropopause altitude of about 11 kilometers, so altitudes of 13 to 17 kilometers suggest that the eruption cloud is mostly in the stratosphere,” said Carn. “The persistence of large SO2 amounts over the last two days also indicates stratospheric injection.”

Volcanologists watch closely for plumes that reach the stratosphere because they tend to stay aloft for longer than those that remain within the troposphere. That is why plumes that reaches the stratosphere typically have the greatest effects on aviation and climate.

NASA Earth Observatory images by Joshua Stevens, using MODIS and VIIRS data from NASA EOSDIS/LANCE and GIBS/Worldview and the Suomi National Polar-orbiting Partnership. Astronaut photograph ISS059-E-119250 was acquired on June 22, 2019, with a Nikon D5 digital camera and is provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit, Johnson Space Center. The image was taken by a member of the Expedition 59 crew. The image has been cropped and enhanced to improve contrast, and lens artifacts have been removed. Story by Adam Voiland, with information from Erik Klemetti (Denison University), Simon Carn (Michigan Tech), and Andrew Prata (Barcelona Supercomputing Center).

The Campi Flegreicaldera cluster is the largest volcanic feature along the Bay of Naples, which is also home to the more famous Vesuvius. The Campi Flegrei, or “Fiery Fields,” is built from a series of overlapping volcanic features—calderas, domes, and cinder cones—that are historically active.

The Campi Flegrei calderas have produced two of the largest eruptions Europe has seen in the past 40,000 years. The Neopolitan Yellow Tuff (rock composed of fragments of material embedded within volcanic ash) was erupted roughly 12,800 years ago, with a total volume of at least 40 cubic kilometers (10 cubic miles). The Campanian Ignimbrite (rock made from the fused remnants of a pyroclastic flow) is about 32,800 years old and has a volume of at least 100 cubic kilometers (20 cubic miles).

Since the Neopolitan Yellow Tuff was formed, numerous small eruptions have occurred in the caldera complex, mostly less than half a cubic kilometer (0.1 cubic miles) in size. The most recent eruption occurred in 1538 at Monte Nuovo, a small cinder cone; that strombolian activity killed at least 32 people.

The most obvious manifestation of the magma under the surface at the Campi Flegrei is the La Solfatara, a region of intense hydrothermal activity. There has also been repeated cycles of uplift and subsidence near the city of Pozzouli, sometimes on the order of meters per decade, along with degassing within the Gulf of Pozzouli.

This natural-color image was acquired by the Advanced Land Imager (ALI) aboard the Earth Observing-1 (EO-1) satellite on July 9, 2012.